Rear Wheels

Looking for some info from anyone with a Demon/Duster, mini-tubbed, with an 8 3/4 and running 17” wheels.

Looking for some backspacing, rear shortening, or combination of both.

Running 17” Magnum 500’s, either a 9.5” or an 11” wide wheel.

Wondering if shortening the rear is even necessary with enough backspace. Also wondering what that backspace would be.

TIA